To prevent the accumulation of scale and other deposits in the cooling tubes of a heat exchanger, especially in a power plant heat exchanger, it is known to introduce into the cooling water, cleaning particles sometimes referred to as cleaning bodies, balls, etc., which may be composed of a synthetic resin material or may be spongy or may have some other surface texture or structure which enables them, as they are entrained by the cooling water, to rub against the surfaces of the pipes which would normally develop accumulations to prevent such accumulations from developing or to remove those accumulations which have developed.
Downstream of the heat exchanger, means is provided to recover such cleaning particles from the water. The present invention is concerned with such means.
It is known to provide in a substantially cylindrical duct, traversed by the cooling water carrying the cleaning particles downstream of the heat exchanger, at least one swingable recovery sieve which may pivot about a transverse axis, i.e. an axis perpendicular to the direction of liquid flow. This sieve which can be made up of spaced-apart mutually parallel bars, generally lying orthogonal to this pivot axis, permits the passage of the particles so that the latter accumulate on the upper surface of the sieve and are guided downwardly to one side of the duct where an outlet is provided from which the particles can be removed, e.g. to be recirculated to a particle feeder at the upstream side of the heat exchanger.
Because the duct is generally vertical and the recovery sieve is inclined to the direction of liquid flow, it generally is of elliptical configuration and lies with its edges on a correspondingly elliptical seat upstream of which the guide elements can be provided to direct the flow onto the central portion of the sieve.
To permit the pivoting movement of the sieve, parts of the flow cross section cannot be formed with the sieve bars.
In other prior art structures, two such sieves can be provided in a gable or roof structure, i.e. the sieves can form an inverted V whereby each sieve is inclined downwardly and outwardly from, for example, a vertical median plane through the duct.
The particles, which are generally spheroidal, are thus filtered from the water traversing the sieve structure and normally will roll downwardly along the sieves. However, while the sieves serve to remove the cleaning particles, in practice they also collect solids which may be scoured by the particles from the pipes, such contaminants tending to accumulate to the sieves.
To remove these particles and contaminants which may be caked up on the sieve and prevent or limit further passage of water, the sieve may be made tiltable so that it can be swung into a position in which the bottom of the sieve is presented to the upstream side and hence the water may wash such contaminants from the surface of the sieve which, in the position into which the sieve is swung, has the contaminant accumulating surface turned downstream.
For the cleaning of the grate or sieve, the supply of cleaning particles is briefly interrupted.
The guide elements previously mentioned are intended to ensure that, in the recovery position of the sieve, the particles can flow and indeed are induced to flow toward the particle outlet and that the movement of the particles on the sieve surface in the region of the outlet is not restricted by impurities entrained by the water and which without such means could detrimentally accumulate on the sieve.
The guide element usually used heretofore was a solid three-dimensional guide body having a crescent shape resembling a slice of a melon which was fixed equidistantly from the sieve seat on the housing wall.
The ends of this guide body were generally pointed.
The space beneath the upstream surface of the guide body was not integrated with the flow. This space, indeed, was generally occupied by part of the guide body or its support.
As a consequence, over a significant portion of the region of the sieve in which the guide body was intended to be effective to generate a movement-promoting effect on the particles, no such effect was noticeable. Indeed, even directly below the guide body, accumulations were found to develop which could impede the movement of the particles along the sieve and from the outlet. Thus, in spite of the guide members utilized heretofore, frequently the discharge of the particles was prevented or limited requiring interruption of the operation of the device.